Windows, including windshields and canopies, in aviation and aerospace vehicles are often made of interlayers and rigid substrates, such as polycarbonates, glass, acrylics, and combinations thereof. These windshields and canopies should maintain long-term optical clarity and structural strength. To that end, primers have been used to increase adhesion between these different layers of windshields and canopies. Traditional primers generally include monomeric siloxane and amino silane based primers.
These traditional primers improve adhesion between different layers of windshield (rigid and flexible parts), but the primer solution may suffer from instability problems. In particular, a traditional primer solution may increase in viscosity, form sediments, or separate over time. This is especially true for concentrated primer stock solutions, which must sometimes even require refrigerated storage or storage under nitrogen. Even under optimal storage conditions, traditional primer stock solutions have a shelf life ranging from a day to a month. Diluting the primer stock solution to lower concentrations may increase the shelf life to up to six months, but this also increases the volume of solution that must be stored.
Moreover, the adhesion strength provided by traditional primers, as measured in pounds per linear inch (“pli”) during a peel strength test, is less than optimal. If the adhesion provided by the primer is insufficiently strong, the layers of the windshields and/or canopies may separate, resulting in delamination. This is a serious safety concern for a pressurized aircraft, as delamination can lead to compromised visibility, chipping, cracks, and window failure.